The train was one of the game-changing inventions that defined the Industrial Age. No more would humanity rely on tempestuous animals to haul goods and passengers great distances across the land. Fire and steam came along to rapidly increase the speed of travel and transformed the very fabric of society itself.

To this day, the vast majority of train networks rely on the same basic principle—heavy locomotives and carriages running steel wheels on steel tracks. Yet, there is a curious alternative twist on this concept that sees trains of carriages riding on tires instead. But what would possess anyone to build a rubber tired train?

Where The Rubber Meets The Rail

The first practical rubber-tired train system came about in the wake of World War II. The Paris metro had been poorly maintained during the German occupation, and was in dire need of repair or replacement. The state-owned public transport operator RATP and tire supplier Michelin came to the table, developing a concept wherein vehicles running on pneumatic tires would ride on a flat steel or concrete  “rollway.” The vehicles would also have backup steel wheels that run against a steel rail for safety, keeping the train upright in the case of a tire blowout. Guidance would be provided by extra rubber tires mounted to the wheel bogies on a vertical axis, running against a vertical guideway built into the track, in a manner not dissimilar from later O-Bahn systems.

By the 1950s, when the concept was being seriously developed, steel-wheeled railways had been around for well over a century. They were the norm for good reason, but running rubber-tired trains did offer some advantages. The pliable tires would soak up vibrations, which was both good for passenger comfort as well as also virtually eliminating high-pitched squealing noises that are common on steel railways. The rubber tires, running on concrete or steel surfaces, also offered greatly improved grip. This allowed the rubber-tired metro trains in Paris to climb much greater grades with ease, compared to traditional steel-wheeled railcars. It also aided in early automation efforts on the Paris Metro, as the higher grip level made it easier to ensure locomotives stopped at the right position when entering stations. Rail wear is also greatly reduced compared to steel-on-steel systems.

Of course, rubber tires also came with some drawbacks. Tracks were more expensive to build due to the need to incorporate both rollways and guideways, and commonly a steel rail to supply electricity to the trains. Rubber tires don’t last as long as steel wheels, either, aren’t as robust, and are subject to blowouts when damaged. The flexing of pneumatic rubber tires also makes the trains less energy efficient, and generates more heat in operation, which can be a concern in underground operations. As tires break down, they also create particulate pollution which isn’t great for urban air quality or for the people breathing it in.

The Paris Metro found the oddball concept to be of great use, particularly given some of the higher grades faced in certain parts of the network. In time, lines 1, 4, 6, 11, and 14 would all be retooled to the Michelin-designed system with rubber-tired railcars running on 1,435 mm rollways. Various airport routes would later adopt rubber tired services, too, as well as the Toulouse, Lille, Lyon, and Marseille metros as well.

The system was not just limited to France, either. Mexico City found a rubber-tired metro to be the perfect transport solution, as the reduced vibrations were a massive boon given the area’s unstable soils. Other famous examples include the Montreal Metro in Canada, and lines 1, 2, and 5 of the Santiago Metro in Chile. Many other smaller-scale examples can be found around the world, often serving airport routes or shorter-distance lines.

Rubber-tired metros are unlikely to ever fully overtake more traditional steel-wheeled trains in popularity. There are more drawbacks than positives for most typical operations, particularly when it comes to maintenance and ongoing costs. Nevertheless, they have their place, particularly where grip is at a premium, grades are steep, or there is a keen desire to avoid excessive noise and vibration to keep the peace or avoid disturbing the subsurface. These rail-like curios stand out as a weird surprise treat for any railfan visiting Paris, or any of the other similar systems that can be found around the world.